The use of polymeric ingredients in compositions, particularly topically administrable ophthalmic compositions, is well known. Polymeric ingredients are typically used in suspension compositions as physical stability aids, helping to keep the insoluble ingredients suspended or easily redispersible. Polymers also impart desirable viscoelastic and rheological characteristics to compositions of which they are a part.
Many polymers have been used in topically administrable ophthalmic compositions. Included among these are cellulosic polymers, such as hydroxypropyl methylcellulose, hydroxyethyl cellulose, and ethylhydroxyethyl cellulose. Also included are synthetic polymers, such as carboxyvinyl polymers and polyvinyl alcohol. Still others include polysaccharides such as xanthan gum, guar gum, and dextran.
Combinations of polymers have also been used in ophthalmic compositions. Certain combinations of polymers are known to provide synergistic effects on viscosity and, in some cases, even a phase transition from a liquid to a gel. For example, U.S. Pat. No. 4,136,173 discloses ophthalmic compositions containing a combination of xanthan gum and locust bean gum.